Seal tag data helps us understand collision risk

Seal tag data helps us understand collision risk

SMRU Consulting are excited to present a new publication on the seal tagging studies carried out at the world’s first commercial scale tidal turbine, SeaGen, at Strangford Lough, Northern Ireland.

This analysis, which was led by our Vancouver based statistician Ruth Joy, really highlights the value of site specific empirical information on behaviour to get a better handle on the risks for marine animals posed by marine energy devices.

We attached tags developed by the Instrumentation group at the Sea Mammal Research Unit to harbour seals before construction and then during operation of the SeaGen tidal turbine. We quantified the risk of collision between the rotating turbine blades and seals by taking into account seal swimming and diving behaviour, tidal state and the physical characteristics of the turbine.

We found evidence of a change in distribution of seals between the pre-construction and the operational period – with the seals tagged after the installation using the area immediately around the operating turbine approximately 68% less than seals had before the construction of the turbine.

We also found that seals spend relatively little time at the same depth as the turbine, appearing to forage on the seabed, travelling between there and the surface to breathe and not spending much time at intermediate depths where they would be more at risk. This was the case both in the presence and the absence of the turbine so appears to be a feature of seal foraging behaviour in the area.

We also made an unexpected observation – that seals were moving slowly, in the opposite direction to the tidal current which may be related to a particular foraging strategy e.g. exploiting prey that is moving with the tide.

By putting all these findings together, we calculated the change in estimated collision risk (using a standard predictive model) was lower than that which would be calculated using standard inputs and assumptions based on uniform (pre-installation) density and behaviour. The total reduction in risk was as much as 90% when site specific detailed information was included.

Although this study provides valuable information on the mid-scale reactions of animals to the presence of turbines, the resolution of the tag data is not fine enough to help us understand the fine detail of how animals behave in close vicinity of operating turbines. To help us understand this better we are currently working on a number of projects both nationally and internationally with our colleagues at The Sea Mammal Research Unit, developing and deploying innovative new monitoring techniques to reduce uncertainty about the potential risks to marine mammals from the tidal energy industry.